End caps are often used on round or rectangular tubular structures to either protect surfaces from the edges of the tubular structures, to protect the end of the tubular structures, or to simultaneously perform both functions. Likewise, objects can be protected from the ends of the tubular structures by the end caps.
End caps can be affixed to the tubular structures in a variety of ways. For example, for threaded tube ends, the end caps may have mating threads and be screwed on to the tube ends. For smooth round tube ends, the end caps may be friction fit by designing the end cap to have an interior diameter that matches (or is slightly smaller than) the outer diameter of the round tube. A similar fitting process can be used for rectangular shaped tubes. Friction fitted end caps, however, tend to be pulled off the tube ends when the tube ends form a base structure and the end caps are used to provide support surfaces for the structure. Examples of such structures are clothing racks for displaying clothes, L-screens, protective screens, pitching screens for baseball and softball coaching, and other structures used in a variety of different settings and that are often moved by being dragged across surfaces.
One solution is to design the end cap to be tightly fitted by under sizing the interior diameter of the end cap; however, attachment and removal of undersized end caps can be difficult. This problem is exacerbated if numerous end caps are replaced frequently.